Sheet feeder

ABSTRACT

A sheet feeder includes: a roller, operable to rotate so as to feed a sheet in a feeding direction; a pad, operable to press the sheet against the roller; and a rotatable presser, having a pressing projection held in contact with a first surface of the pad and a pressing surface held in contact with a second surface of the pad. The second surface is larger than the first surface in the feeding direction, and the pressing projection is arranged at a downstream side of the pressing surface in the feeding direction.

BACKGROUND OF THE INVENTION

The present invention relates to a sheet feeder which feeds sheets of sheet to an apparatus such as a printer or a scanner, and particularly to a sheet feeder which realizes a reliable consecutive sheet feeding without an occurrence of multiple feeding or jams.

In a related sheet feeder, when sheets stacked on a stacker are picked by a pick roller, as shown in FIG. 4, a configuration has been such that sheets 54 are inserted between a pick roller 50 and a separation pad 51, and the sheets are transported one by one into an apparatus using a frictional force.

In this case, a configuration is such as to include a pad pressing unit 52 which applies a pressure for bringing the separation pad 51 into contact with a surface of the pick roller 50 by means of a pressure spring 53 in order to bring the separation pad 51 into contact with the pick roller 50 in such a way that a sufficient frictional force acts between the pick roller 50 and the separation pad 51.

However, with such a structure in which a pressure is supplied to one point, an area in which the separation pad 51 makes contact with the pick roller 50 is inevitably narrowed, and the separation pad 51 cannot completely separate a plurality of bundled sheets, causing a multiple feeding in some cases.

Accordingly, as shown in FIG. 5, there is a related sheet feeder which the pad pressing unit 52, which applies a pressure to the separation pad 51, is formed in an inverted U-shape, thereby enabling the separation pad 51 to press against the surface of the pick roller 50 at two points, and an area in which the separation pad 51 makes contact with the pick roller 50 is widened, thereby enabling the sheets to be reliably separated one from another (for example, refer to JP-A-8-91609).

However, even with such a structure, depending on a type of sheet, a pressure distribution is not uniform at two front and back points of the pad pressing unit 52 due to the fact that the sheets 54 make contact with the separation pad 51, and it has sometimes been impossible to effectively separate the sheets one from another.

Accordingly, in order to solve such problems, as shown in FIG. 6, there is a related sheet feeder in which the pad pressing unit 52 includes a first pad pressing member 52 a and a second pad pressing member 52 b, being equipped respectively with a first rotation fulcrum 55 and a second rotation fulcrum 56, wherein the second rotation fulcrum 56 is provided in a center of the second pad pressing member 52 b, and the second pad pressing member 52 b is made rotatable back and forth with respect to a rotation direction of the pick roller 50, whereby a pressure distribution is made uniform at two front and back points of the second pad pressing member 52 b (for example, refer to JP-A-2006-96503).

However, practically, even with such a structure, as the separation pad 51 has a rigidity, at a portion P1 in the figure, a reaction force of the separation pad 51 to bring the separation pad 51 into contact with the pick roller 50 is in inverse proportion to the cube of L1, while, at a portion P2, it is inversely proportional to the cube of L2. Consequently, under pressures having a relationship P1=P2, an urging force by P2, which presses the separation pad 51 against the pick roller 50, is considerably reduced, and there has been a problem in that a concentric load is conversely applied to the portion P1.

SUMMARY

It is therefore an object of the invention to provide a sheet feeder which, being used in an apparatus such as a printer or a scanner, automatically transports sheets into the apparatus, wherein, regardless of a type of the sheets stacked on a stacker, the stacked sheets are reliably transported, one at a time, into the apparatus.

In order to achieve the object, according to the invention, there is provided a sheet feeder comprising:

a roller, operable to rotate so as to feed a sheet in a feeding direction;

a pad, operable to press the sheet against the roller; and

a rotatable presser, having a pressing projection held in contact with a first surface of the pad and a pressing surface held in contact with a second surface of the pad, wherein

the second surface is larger than the first surface in the feeding direction, and

the pressing projection is arranged at a downstream side of the pressing surface in the feeding direction.

With this configuration, the pad and the roller can secure a sufficient contact area for a sheet separation. Furthermore, even in consideration of deflection characteristics due to a rigidity of the pad, a pressure distribution is made uniform in the contact area between the pad and the roller, making it possible to separate the sheets one from another regardless of a type of sheet.

The pressing surface may have a shape that resembles a mating surface of the pad.

The pad may include a portion having a shape that resembles a peripheral surface of the roller.

The roller may have a first peripheral layer and a second peripheral layer inside of the first peripheral layer. Both the first peripheral layer and the second peripheral layer may be comprised of a rubber. The first peripheral layer may be greater than the second peripheral layer in a durability. The first peripheral layer may have a higher friction coefficient than the second peripheral layer. The first peripheral layer may be greater than the second peripheral layer in a hardness.

In this case, it is possible to obtain the roller having a low hardness and an excellent abrasion resistance, enabling a more reliable sheet separation process.

The sheet feeder may further comprise a holder, operable to hold the presser rotatably.

In order to achieve the object, according to the invention, there is also provided a sheet feeder comprising:

a roller, operable to rotate so as to feed a sheet in a feeding direction;

a pad, operable to press the sheet against the roller; and

a presser, operable to rotate around a rotational point, and having a first projection operable to press the pad at a downstream side in the feeding direction and a second projection operable to press the pad at an upstream side in the feeding direction, wherein

the rotational point is displaced to a downstream side in the feeding direction from a center point between the first projection and the second projection.

With this configuration, the pad and the roller can secure a sufficient contact area for a sheet separation. Also, as the rotational point of the presser is off-centered toward a front end of the pad, in accordance with the principle of leverage, a concentric load is applied to the front side of the pad, and only a weak force is applied to the back side the pad. For this reason, in consideration of deflection characteristics due to a rigidity of the pad, a pressure distribution is made uniform in the contact area between the pad and the roller, making it possible to reliably separate the sheets one from another regardless of a type of sheet.

The presser may have an inverted U-shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an example 1 of the invention;

FIG. 2 is an example 2 of the invention;

FIG. 3 is an illustration of a pick roller configured in a two-layer structure;

FIG. 4 is an illustration of a related separation pad pressing unit;

FIG. 5 is an illustration of a case in which a related inverted U-shape pad pressing unit is used; and

FIG. 6 is an illustration 2 of a case in which a related inverted U-shape pad pressing unit is used.

DETAIL DESCRIPTION OF PREFERRED EMBODIMENTS

A description will be given, with reference to the drawings, of representative examples according to the invention. Hereafter, the same parts are indicated by identical numerals, and a detailed description may be omitted.

In an automatic sheet feeder of the example 1 of the invention (as shown in FIG. 1), a pick roller 1 for picking sheets stacked on a stacker is equipped with a separation pad 2 for separating the sheets one from another and, by a force being applied in a direction in which the separation pad 2 is pressed against the pick roller 1, a frictional force acts on the sheets passing between them, and the sheets are separated one from another.

At this point, in order to make the sheets easily separated from one another, it is necessary that, as well as the separation pad 2 and the pick roller 1 securing a sufficient contact area, an urging force is applied uniformly to the whole contact area.

Accordingly, as shown in FIG. 1, by configuring pad pressing unit 3 in such a way that a pressure spring 4 causes a second pad pressing member 3 b to apply a force in a direction in which the separation pad 2 is pressed against the pick roller 1, and that the second pad pressing member 3 b rotates back and forth around a second rotation fulcrum 6 with respect to a rotation direction of the pick roller 1, forces applied to the front and back of the second pad pressing member 3 b are made uniform. Also, in consideration of deflection characteristics due to a rigidity of the separation pad 2, the second pad pressing member 3 b is formed in a shape in which a front end thereof (at a downstream side) has a projection, and a rear end thereof (at an upstream side) presses the separation pad in a surface-to-surface contact relationship in which it rubs an underside of the separation pad 2. The rear end of the second pad pressing member 3 b has a shape that resembles the underside of the separation pad 2. A contact area between the rear end of the second pad pressing member 3 b and the separation pad 2 is lager than a contact area between the projection of the second pad pressing member 3 b and the separation pad 2. So that, a distal end of the separation pad 2 (at a downstream side) is bended so as to follow a shape of the pick roller 1.

When a very thick sheet enters, by a first pad pressing member 3 a rotating the whole pad pressing unit 3 around a first rotation fulcrum 5, it is possible to maintain an appropriate pressure without an unreasonable force being applied to the separation pad 2.

In the same way as in the example 1, in the example 2 of the invention (as shown in FIG. 2), by the second pad pressing member 3 b being formed in a shape in which its second rotation fulcrum 6 is off-centered toward the front end of the separation pad 2 in such a way that the urging force is applied uniformly to the whole area in which the separation pad 2 and the pick roller 1 are in contact with each other, a relationship L1>L2 is obtained, and P1<P2 is established from the principle of leverage. Here, the second pad pressing member 3 b has an inverted U-shape. As such, a load concentrates on a front side edge of the second pad pressing member 3 b, meaning that little force is applied to a rear side edge and, in consideration of deflection characteristics due to a rigidity of the separation pad 2, a uniform urging force is applied to the whole contact area between the separation pad 2 and the pick roller 1.

In such an automatic sheet feeder made up of a combination of the separation pad and the pick roller, in order to carry out a more reliable sheet separation, as shown in FIG. 3, it is also acceptable to configure the pick roller 1 in a two-layer structure in which a rubber member having a high durability and a high friction coefficient is used as an outer layer 1 a, and a low hardness foamed rubber member made of interconnected cells having a low compressive residual stress is used as an inner layer 1 b.

In this case, the pick roller uses a rubber member having a rubber hardness of 20 degrees (JIS-A) or less.

According to an aspect of the invention, in consideration of deflection characteristics due to a rigidity of the separation pad, by securing a sufficient contact area between the separation pad and the pick roller, as well as a pressure distribution in the contact area becoming uniform, it becomes possible to provide an automatic sheet feeder which can reliably feed sheets of any type, one at a time, into an apparatus. 

1. A sheet feeder comprising: a roller, operable to rotate so as to feed a sheet in a feeding direction; a pad, operable to press the sheet against the roller; and a rotatable presser, having a pressing projection held in contact with a first surface of the pad and a pressing surface held in contact with a second surface of the pad, wherein the second surface is larger than the first surface in the feeding direction, and the pressing projection is arranged at a downstream side of the pressing surface in the feeding direction.
 2. The sheet feeder according to claim 1, wherein the pressing surface has a shape that resembles a mating surface of the pad.
 3. The sheet feeder according to claim 1, wherein the pad includes a portion having a shape that resembles a peripheral surface of the roller.
 4. The sheet feeder according to claim 1, wherein the roller has a first peripheral layer and a second peripheral layer inside of the first peripheral layer, both the first peripheral layer and the second peripheral layer are comprised of a rubber, the first peripheral layer is greater than the second peripheral layer in a durability, the first peripheral layer has a higher friction coefficient than the second peripheral layer, and the first peripheral layer is greater than the second peripheral layer in a hardness.
 5. The sheet feeder according to claim 1 further comprising: a holder, operable to hold the presser rotatably.
 6. A sheet feeder comprising: a roller, operable to rotate so as to feed a sheet in a feeding direction; a pad, operable to press the sheet against the roller; and a presser, operable to rotate around a rotational point, and having a first projection operable to press the pad at a downstream side in the feeding direction and a second projection operable to press the pad at an upstream side in the feeding direction, wherein the rotational point is displaced to a downstream side in the feeding direction from a center point between the first projection and the second projection.
 7. The sheet feeder according to claim 6, wherein the presser has an inverted U-shape.
 8. The sheet feeder according to claim 6, wherein the roller has a first peripheral layer and a second peripheral layer inside of the first peripheral layer, both the first peripheral layer and the second peripheral layer are comprised of a rubber, the first peripheral layer is greater than the second peripheral layer in a durability, the first peripheral layer has a higher friction coefficient than the second peripheral layer, and the first peripheral layer is greater than the second peripheral layer in a hardness.
 9. The sheet feeder according to claim 6 further comprising: a holder, operable to hold the presser rotatably. 